1. Field of the Invention
The present invention comprises a process and system for efficiently separating, collecting and removing metallic radioactive elements (nucleides) from predominantly solid, non-metallic bulk low-grade nuclear waste.
2. Description of Related Art
Nuclear waste is comprised of many different kinds of radioactive materials. These materials are classified into different types, called waste forms. Each waste form has specific characteristics that require certain methods of treatment and storage. A variety of techniques and methods have to be applied to treat components of nuclear waste.
Radioactive nuclear waste can be grouped into four categories, namely, high-level waste, transuranic waste, low-level waste, and uranium mill tailing.
Radioactive waste management is the treatment and containment of radioactive waste. The number one aim in the safe handling and containment of radioactive waste is the prevention of radiation damage to humans and the environment by controlling the dispersion of radioactive materials. Nuclear waste management is mainly controlled by policies of the United States government. Because of the expected increase in quantities of waste containing materials or those contaminated with transuranic elements, and because of the long half life and specific radioactive toxicity of these elements, the U.S. government policy requires that most transuranic waste must be solidified. A variety of technologies exist for this conversion including calcination, vitrification, oxidation, and metallurgical smelting depending on the primary waste.
A typical solidification process chiefly for all forms of waste is spray calcination-vitrification. In this process, atomized droplets of waste fall through a heated chamber where flash evaporation results in solid oxide particles. Glass making solid frit or phosphoric acid can be added to provide for melting and glass formation either in a continuous melter or in the vessel that will serve as the waste canister. The molten glass or ceramic is cooled and solidified.
Ironically using these processes increases the volume of waste material that has to be disposed and stored somewhere. Vitrification processes are also expensive to operate.
The present invention greatly increases the efficiency of treating and storing low grade nuclear waste while significantly reducing the volume of material that must be stored because of its radioactive toxicity at a great cost savings.
Vitrification has not been a good solution because it actually increases the volumes of solids that have to be stored safely. Using the present invention, it is believed that 95 to 99% volume of the low grade nuclear bulk waste can be restored safely to the environment eliminating the need for expensive large volume bulk storage.
The present invention comprises a process and system for use with transuranic and low-level nuclear waste to separate metallic radioactive materials from the low-grade bulk non-metallic waste, allowing the radioactive elements to be separated, lifted away, captured, and concentrated into a smaller volume, leaving the remaining non metallic bulk waste non-radioactive and ready for free release into the environment after a full processing cycle, or less radioactive and ready for more conventional waste handling after a partial cycle.
The process and system are specifically ideal for dry, non-metallic, low-grade nuclear waste containing transuranic radioactive elements or other radionucleides making up one particle per million (PPM) (or less) particulate density.
Several complex methods are shown in the prior art for separating nuclear materials. U.S. Pat. No. 3,629,135 issued to Wilding, Dec. 21, 1971, shows a method of dissolving radioactive contaminated organic ion exchange resins by heating the resin in a solution of nitric acid and potassium permanganate.
U.S. Pat. No. 3,893,845 issued to Mahaffey, et al, Jul. 8, 1975, shows a method for reducing matter to constituent elements and separating one of the elements from the other elements. Basically, this is accomplished in a high temperature environment (plasma). The reduction is caused by raising the input compound to a high temperature so that the input compound is thermally dissociated. This can also be affected by chemically reducing the compound to a gas consisting of a specie or element which can be more readily ionized and another product of the chemical reduction reaction. Separation therefore is effected by partly ionizing one of the species to be separated and moving the resultant mixture of gas and plasma through a magnetic field shaped to increase intensity in direction flow of the gas and plasma. The plasma is squeezed by the magnetic field creating a force on the ionized specie only, producing separation.
U.S. Pat. No. 5,523,514 issued to Cauquil, Jun. 4, 1996, shows a process for dissolving plutonium and other radioactive elements that are present in solid or liquid products by microwave heating. The process also uses solutions of toxic nitric acid and hydrofluoric acid.
U.S. Pat. No. 5,681,434, issued to Eastlund, Sep. 28, 1997, shows a method and apparatus for ionizing all the elements in a complex substance such as radioactive waste and separating some of the elements from other elements. The principle method used is again high temperature plasma confined by toroidal magnetic fields. One method utilizes plasma (high temperatures) confinement by toroidal magnetic fields as a gate to regulate when and where specific elements are collected. The apparatus is a large volume plasma processor with multiple containment vessels. The system requires tremendous amounts of heat energy.
The use of the present invention for separating radioactive materials from non-metallic bulk waste does not employ high temperature plasma requirements or the use of toxic chemicals. Metallic radioactive materials at the (micron size) level can be separated from large volumes of non-metallic low grade nuclear waste, collected and concentrated together in a significantly smaller volume, and safely stored efficiently and economically in accordance with the present invention.